The present disclosure relates generally to hybrid, off-highway vehicle (OHV) and trolley systems and, more particularly, to a method and system for optimizing energy storage in hybrid off-highway vehicle and trolley connected OHV systems.
Off-highway (OHV) vehicles, including trolley connected OHVs and other large traction vehicles, are commonly powered by electric traction motors coupled in driving relationship to one or more axles or motor-wheel sets of the vehicle. In the motoring or traction mode of operation, the traction motors are supplied with electric current from a controllable source of electric power (e.g., an engine-driven traction alternator/rectifier/inverter combination or, alternatively, a direct current drive source including a dc motor without an inverter) and apply torque to the vehicle wheels which exert tangential force or tractive effort on the surface on which the vehicle is traveling (e.g., a haulage track or road), thereby propelling the vehicle in a desired direction along the right of way.
Conversely, in an electrical (i.e., dynamic) braking mode of operation, the same motors serve as axle-driven/wheel-driven electrical generators. Torque is applied to the motor shafts by their respectively associated axle-wheel sets which then exert braking effort on the surface, thereby retarding or slowing the vehicle's progress. Because there is no suitable storage medium for the resulting generated electrical energy in a conventional off-highway vehicle or trolley connected OHV, an electrically resistive grid (known as a dynamic braking grid or load box) is used to convert the electrical energy into heat energy, which is then vented to the atmosphere.
In contrast, hybrid OHVs and hybrid trolley connected OHVs have the capability of storing the generated dynamic braking energy in a suitable storage element(s) such as batteries, flywheels, ultracapacitors and the like,. This stored energy may then be used for traction and/or auxiliary systems in the OHV, thereby improving fuel efficiency. However, regardless of whether an OHV includes power storage elements and/or energy dissipative elements, such components contribute to the overall size and weight of the vehicle and thus to the costs of the vehicle. As such, it is desirable to be able to provide an OHV with energy storage capability for fuel savings while also reducing the size of the associated components (e.g., engine and dynamic brake resistors, etc.), which could then result in greater payload capability.
In addition, trolley connected OHVs should also have full engine capability in order to motor around breaks in the trolley line (as well as around other OHVs that may have broken down), and also to maneuver in or around haul road sections, loading and unloading areas, and maintenance facilities where the trolley lines have not been provided. A trolley line may also be electrically weak at the ends of the line where it is unable to provide full OHV motoring power requirement, thereby necessitating the use of the diesel engine. In a dynamic braking mode, if the trolley connected OHV send braking energy back onto the trolley line, another trolley connected OHV must be available to used/dissipate the energy. Otherwise, the braking energy must be dissipated in the trolley connected OHV's braking grid.
Thus, for trolley connected OHVs, it is further desirable to be able to reduce the engine and/or braking grid sizes, while still maintaining full motoring and braking capability, in the event that the trolley line is unable to provide the full OHV energy requirement and/or accept the full OHV braking energy generation.